Does not work with ~/.cargo/bin not being the most important path

[nagisa]

It manifests itself in two ways:

$ ~/.cargo/bin/rustup run nightly cargo build --release
   Compiling permutohedron v0.2.1
   Compiling itertools v0.4.13
   Compiling fixedbitset v0.1.0
error: the crate `std` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `core` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `collections` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `rustc_unicode` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `alloc` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `rand` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `libc` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `alloc_jemalloc` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `std` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `core` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `collections` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `rustc_unicode` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `alloc` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `rand` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `libc` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `alloc_jemalloc` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: aborting due to 8 previous errors
error: the crate `std` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `core` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `collections` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `rustc_unicode` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `alloc` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `rand` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `libc` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
error: the crate `alloc_jemalloc` has been compiled with rustc 1.10.0-nightly (d91f8ab0f 2016-05-07), which is incompatible with this version of rustc [E0514]
help: consider removing the compiled binaries and recompiling with your current version of rustc
Build failed, waiting for other jobs to finish...
error: aborting due to 8 previous errors
error: aborting due to 8 previous errors
error: Could not compile `permutohedron`.

To learn more, run the command again with --verbose.

when there’s a local copy of rustc in /usr/

and

$ ~/.cargo/bin/rustup run nightly rustc --version
rustc 1.10.0-nightly (5ebe41835 2016-05-15)                 
$ ~/.cargo/bin/rustup run nightly cargo --version
error: Could not execute process `rustc -vV` (never executed)

Caused by:
  No such file or directory (os error 2)

when the local copy is removed.

[brson]

If we want rustup to take precedence over the system rustc (which may be the right thing to do), then the setup_mode will need to prepend it to the PATH and so will the proxies.

[brson]

Currently setup prepends the ~/.cargo/bin path, and the proxies append ~/.cargo/bin and the toolchain path.

Offhand I can't remember why the proxies append instead of prepend, and I can't think of a reason, so let's just change it and see what happens! Modify Toolchain::set_ldpath and include a link to this issue so I don't forget again.

[Diggsey]

This should have been fixed in #707

[Kouloum04]

install ~/.cargo/bin